This invention relates generally to the field of telecommunication systems, and more particularly to a transmission slot allocation method and map for virtual tunnels in a transmission line.
Telecommunications networks have traditionally been circuit-switch networks that have transmission paths dedicated to specific users for the duration of a call and that employ continuous, fixed-bandwidth transmission. Due to growth in data traffic created by the Internet and its related technologies, however, telecommunications networks are being moved to a packet-switching transmission model. Packet-switch networks provide a large range of digital services, from data to video to basic voice telephony. Packet-switch networks can allow dynamic bandwidth and may be connectionless with no dedicated path or connection-oriented with virtual circuits and dedicated bandwidth along a predetermined path.
Asynchronous transfer mode (ATM) is a connection-oriented packet-switching technology in which information is organized into small, fixed length cells. ATM carries data asynchronously, automatically assigning data cells to available time slots on demand to provide maximum throughput. Compared with other network technologies, ATM provides large increases in maximum supported bandwidth, designed-in isosynchronous traffic support, support for multiple types of traffic such as data, video, and voice transmissions on shared communication lines, and virtual networking capabilities, which increase bandwidth utilization and ease network administration.
ATM cells are routed through a telecommunications network at high speeds using a switching label included in the cell. The switching label has two sections that define a virtual path (VP) and a virtual channel (VC) in the network through which the cell is routed. The use of virtual paths and virtual channels allows physical bandwidth in the network to be subdivided and separately commercialized.
Because of the low latency and predictability throughput ATM offers, it is capable of providing quality of service (QoS) features. QoS is defined in terms of the attributes of end-to-end ATM connections and is important in an integrated service network, particularly for delay-sensitive applications such as audio and video transmissions, as well as voice-over IP. Other applications in which QoS may be important include traditional data communications, imaging, full-motion video, and multimedia, as well as voice.
Performance criteria for describing QoS for a particular connection include cell loss rate (CLR) , cell transfer delay (CTD), and cell delay variation (CDV). ATM traffic is classified as either constant bit rate (CBR) traffic, real-time or non real-time variable bit rate (VBR) traffic, available bit rate (ABR) traffic, and unspecified bit rate (UBR) traffic, depending on the QoS parameters applied to the traffic. CBR and VBR traffic utilize dedicated bandwidth and are intended for real time applications. ABR traffic is intended for non-real time applications which can control, on demand, their transmission rate in a certain range. Like ABR, UBR traffic is intended for non-real time applications which do not have any constraints on the cell delay and cell delay variations.
For CBR, VBR, and other traffic having dedicated bandwidth, transmission slots can be spaced throughout a frame in the transmission line to minimize cell delay variation. However, ABR, UBR, and other types of dynamic bandwidth traffic are evaluated based on transmission line constraints and transmitted in time slots as they become available. As a result, such traffic typically has a high cell delay variation.
The present invention provides a transmission slot allocation method and map that substantially eliminate or reduce the disadvantages and problems associated with previous systems and methods. In particular, the map stores predefined sets of interleaved port transmission slots that can be assigned to dedicated or dynamic bandwidth traffic.
In accordance with one embodiment of the present invention, a map of transmission slots for a port of a network element includes a plurality of hierarchical sets of port transmission slots. The hierarchical sets include a plurality of parent sets. Each parent set has its port transmission slots divided between a plurality of child sets. The child sets include interleaved port transmission slots.
More specifically, in accordance with a particular embodiment of the present invention, the hierarchical sets each include substantially evenly spaced port transmission slots. In this and other embodiments, each parent set is divided into a same number of child sets. The hierarchical sets may also include a plurality of base sets each having a number of port transmission slots corresponding to a base transmission rate for the port.
Technical advantages of the present invention include providing an improved method and map for allocating bandwidth of a transmission line to a virtual interface. In particular, port transmission slots are grouped into a plurality of hierarchical sets having interleaved port transmission slots. The hierarchical sets can be dynamically allocated to a virtual interface to provide transmission slots for any supported bandwidth. In addition, the transmission slots in each set are substantially evenly spaced throughout the transmission frame of the port. This provides minimal delay variation for both dedicated and dynamic bandwidth traffic, and for multiple virtual interfaces operating at different rates. The hierarchical sets are also sized to be equal to or only slightly larger than a supported transmission rate. As a result, allocatable bandwidth is maximized.